Multi-layer substrate for semiconductor packaging

ABSTRACT

The present invention provides a semiconductor substrate ( 105, 105   a ) comprising two or more layers of built-up structural layers ( 120, 220 ) formed on a sacrificial carrier ( 110 ). Each built-up structural layer, comprising a conductor trace layer ( 114   a ,) and an interconnect ( 118   a,    218   a ), is molded in a resin molding compound. A top surface of the molded compound is abrasively ground and then deposited with an adhesion layer ( 123, 124, 224 ). A multi-layer substrate ( 105, 105   a ) is then obtained after an outermost conductor trace layer ( 128   a,    228   a ) is formed on the adhesion layer and the carrier ( 110 ) or reinforcing ring ( 110   b ) is removed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.14/387,843, filed Sep. 25, 2014, which is a National Stage ofInternational Application No. PCT/SG2013/000119, filed Mar. 26, 2013,which claims the benefit of Provisional Application No. 61/615,399,filed Mar. 26, 2012.

FIELD OF INVENTION

The present invention relates to multi-layer substrates forsemiconductor packaging and methods of manufacturing such substrates.

BACKGROUND

Conventional semiconductor dies are mounted on leadframes. Theseleadframes are usually formed by coating a copper substrate with aphotoresist layer, exposing a pattern on the photoresist layer using amask, positively or negatively removing the photoresist layer and thenetching away the copper to give a patterned leadframe. However, such apatterned leadframe formed by etching is not suitable for use with diesthat require finer and closer interconnecting traces than conventionalleadframe. Etching inherently causes undercutting and fine conductivetraces thus formed may have reliability issue for high throughputmanufacturing.

U.S. Pat. No. 7,795,071, assigned to Advanpack Solutions, describes amethod for forming a single-layer patterned substrate for semiconductorpackaging. A gang of patterned conductor layouts is formed on a steelcarrier, and insulating material is injected in a mold to seal theconductive traces. After removing the steel carrier, a substratecontaining a gang of patterned conductor layouts, is formed.Advantageously, the patterned conductor layouts are electricallyisolated from each other, whereas on a conventional leadframe, eachconductor layout corresponding to each die is electrically connected toan adjacent layout.

It can thus be seen that there exists a need to form a multi-layersubstrate with more complex routing of conductive traces to supportfuture designs of integrated circuits. Advantageously, these multi-layersubstrates allow separate conductor layers to be used for signal, power,digital, analogue circuits and so on.

SUMMARY

The following presents a simplified summary to provide a basicunderstanding of the present invention. This summary is not an extensiveoverview of the invention, and is not intended to identify key featuresof the invention. Rather, it is to present some of the inventiveconcepts of this invention in a generalised form as a prelude to thedetailed description that is to follow.

The present invention seeks to provide substrates containing two or morebuilt-up structural layers formed on a sacrificial carrier. Eachbuilt-up structural layer comprises a conductor trace layer and aninterconnect layer. Each built-up structural layer is molded in a resincompound. The multi-layer substrate is then completed by forming anoutermost conductor trace layer and removing the carrier.

In one embodiment, the present invention provides a multi-layersubstrate comprising: a sacrificial carrier that is electricallyconductive and chemically etchable; a first conductor trace layer formedon the sacrificial carrier; a second conductor trace layer and aninterconnect layer disposed between the first and second conductor tracelayers, wherein studs connect selected areas between the first andsecond conductor trace layers.

In one embodiment of the multi-layer substrate, the first conductortrace layer and interconnect layers are encapsulated in a resin moldingcompound. The top surface of the resin molding is abrasively ground andan adhesion layer is deposited on the ground surface. The adhesion layermay be a conductor seed layer, a polyimide layer or a woven glass fiberlaminate. The multi-layer substrate thus comprises two or more built-uplayers, each of the built-up layer is made up of a conductor tracelayer, an interconnect layer and an adhesion layer, such that theoutermost layer is a conductor trace layer.

In another embodiment, the present invention provides a method formanufacturing multi-layer semiconductor substrates. The methodcomprises: forming a first conductor trace layer on a sacrificialcarrier, wherein the first conductor trace layer contains a plurality ofconductor layouts; forming an interconnect layer on the first conductortrace layer, wherein the interconnect layer comprises studs that connectwith selected areas of the first conductor trace layer; encapsulatingthe first conductor trace and interconnect layers in a resin moldingcompound; abrasively grinding a surface of the molded encapsulation forplanarity and to expose the interconnect studs; depositing an adhesionlayer on the ground encapsulation surface; repeating the above steps toform an additional built-up structure of the multi-layer substrate sothat there are 2 or more built-up structural layers; and forming anoutermost conductor trace layer on the top adhesion layer.

In another embodiment, the method further comprises: sealing theoutermost conductor trace layer with an insulating layer; selectivelyremoving the insulating layer to expose areas of the outermost conductortrace layer for external electrical connection.

Preferably, an internal portion of the carrier is removed to leave areinforcing ring around the substrate or a gang of conductor layoutscontained in the first conductor trace layer. Preferably, the firstconductor trace layer is sealed with a soldermask and selective removalof the solder mask exposes areas on the first conductor trace layer forexternal electrical connection.

BRIEF DESCRIPTION OF THE DRAWINGS

This invention will be described by way of non-limiting embodiments ofthe present invention, with reference to the accompanying drawings, inwhich:

FIGS. 1A-1J illustrate structures of a two-layer substrate according toan embodiment of the present invention;

FIGS. 2A-2D, 3 and 4 illustrate methods for forming semiconductorpackages using the multi-layer substrate shown in FIG. 1J;

FIGS. 5 and 6 illustrate structures of a two-layer substrate accordingto another embodiment of the present invention;

FIGS. 7A-7F illustrate structures of a three-layer substrate accordingto yet another embodiment of the present invention; and

FIG. 8 illustrates a plan view of a finished substrate obtainedaccording to the present invention.

DETAILED DESCRIPTION

One or more specific and alternative embodiments of the presentinvention will now be described with reference to the attached drawings.It shall be apparent to one skilled in the art, however, that thisinvention may be practised without such specific details. Some of thedetails may not be described at length so as not to obscure theinvention. For ease of reference, common reference numerals or series ofnumerals will be used throughout the figures when referring to the sameor similar features common to the figures.

FIGS. 1A-1J show progressive build-up of a multi-layer substrate 105comprising two conductor trace layers according to an embodiment of thepresent invention. As shown in FIG. 1A, the first step in the process100 is to provide a carrier 110 having a first surface and an oppositefacing second surface. Preferably, the carrier 110 is made of a low-costmaterial having high Young's modulus of elasticity, is electricallyconductive and is suitable for chemical etching, such as steel. Theseproperties of the carrier 110 allow it to be sacrificially removedpartially during fabrication of the multi-layer substrate 105 and/orcompletely after a semiconductor die 10 is encapsulated. Preferably, thecarrier 110 is stress-relieved or partially stress-relieved, forexample, by annealing.

Subsequent process steps involve coating a surface of the carrier 110with a photoresist, exposing the photoresist with a mask, selectivelyetching away the photoresist, and obtaining a patterned photoresist. Bydepositing a first electric conductor material 114, such as copper, overthe patterned photoresist and then removing the photoresist, a patternedfirst conductor trace layer 114 a is formed on the carrier 110. Thepatterned first conductor trace layer 114 a thus contains a plurality offirst conductor layouts for connection with some semiconductor dies.Preferably, the first conductor material 114 is copper and a suitabledepositing process is electroplating. FIG. 1B shows an enlarged part ofa section through the first conductor trace layer 114 a. For easierreferencing, the patterned first conductor trace layer and the firstconductor layouts are identified by the same reference numeral 114 a. Bysimilar photolithographic process and by depositing a second electricconductor material 118 on a resulting patterned photoresist defininginterconnecting vias, a first interconnect layer 118 a made up ofconductor studs 118 is thus formed on the first conductor trace layer114 a, as shown in FIG. 1C. Alternatively, the first conductor tracelayer 114 a and first interconnect layer 118 a are formed by subtractivephotolithographic processes. Various combinations of additive,semi-additive or semi-subtractive processes can be adopted to create therequired patterned structure. To electrically isolate the conductortraces and to encase the conductor traces/studs in an insulatingmaterial, a gang of the first conductor layouts 114 a and conductorstuds 118 a is disposed in a cavity or gangs of the first conductorlayouts 114 a and conductor studs 118 a are disposed in a plurality ofcavities. An insulating or dielectric molding compound, preferablypreheated to a fluid state, is injected into the cavity or cavities at amelt temperature. Preferably, the fluid molding compound is injected ata positive pressure so that the molding compound is densely packed withthe gang of the first conductor layouts 114 a and conductor studs 118 ato form a compact composite structure or a first insulator layer 120after the molding compound has solidified; as a result, the moldingcompound bonds strongly onto the first conductor layouts 114 a andconductor studs 118 a such that during wet processing, fluid cannotenter the conductor-molding compound interfaces. A semi-finishedsubstrate, as shown in FIG. 1D, is thus obtained. Preferably, the firstinsulator layer 120 comprises a molding compound containing a matrix ofresin and silica fillers. Preferably, after the first insulator layer120 is formed, the silica fillers are embedded within the resin.

The semi-finished substrates shown in FIG. 1D are moved to a machiningcentre and the free surface of the first insulator layer 120 is madeplanar by abrasive grinding, to a depth when all the conductor studs 118a are exposed on the ground surface 122, as shown in FIG. 1E.Preferably, the exposed surfaces of the conductor studs 118 a areleveled with or recessed in the rear surface of the first insulatinglayer 120 (as seen in FIG. 1E) such that the first insulating layer 120defines the edges of the conductor studs and isolates the conductorstuds one from one another. After grinding, the silica fillers in themolding compound are also exposed. Specifically, the ground surface 122now comprises resin interposed with silica fillers; the ground surface122 was found to provide strong adhesion for depositing a conductor seedlayer 124, as shown in FIG. 1F. Alternatively, by increasing the rate ofmaterial removal during abrasive grinding, the surface silica fillersare extracted from the resin to form a plurality of dimples on theground surface 122. The dimpled ground surface 122 provides an increasedsurface area to improve adhesion buildup of the next adjacent layer.When the first conductor material 114 is copper, the conductor seed 124material is also copper. Suitable methods for depositing the copper seedlayer 124 are electroless plating, electrolytic plating, sputtering, CVDor PVD.

By using the photolithographic process, a patterned photoresist is thenformed on the conductor seed layer 124 and by electroplating copper onthe patterned photoresist, a patterned second conductor trace layer 128a is obtained, as shown in FIG. 1G. The second conductor trace layer 128a is made up of a plurality of second conductor layouts 128 a; each ofthese second conductor layouts 128 a is therefore electrically connectedto each of the associated first conductor layouts 114 a through theassociated first conductor studs 118 a.

As shown in FIG. 1H, the patterned second conductor trace layer 128 a iscompleted by sealing it with a second insulating or dielectric layer130. Preferably, the second insulating layer 130 is a soldermaskcontaining a photo imageable polymer material. Preferably, the secondinsulating layer 130 is screen printed onto the patterned secondconductor trace layer 128 a. The second insulating layer 130 is thenexposed to radiation, such as laser radiation, through a mask, and byselective removal, selected areas 128 b of the second conductor tracelayer 128 a are exposed for external electrical connection, as shown inFIG. 1I. Further processing on the exposed second conductor trace layer128 b for solderability may include depositing a tin layer or anickel/gold layer.

As shown in FIG. 1I, the carrier 110 is larger than the molded firstinsulator layer 120. Advantageously, an internal portion 110 a of thecarrier 110 is partially sacrificed and removed, for example by etching,so that a ring 110 b remains and a finished substrate 105 is obtained,as shown in FIG. 1J. After removing the carrier 110, the first conductorlayouts 114 a are exposed together with the surface of the firstinsulator layer 120. Preferably, the surfaces of the first conductorlayouts 114 a are leveled or recessed in the top surface of the firstinsulator layer 120 (as seen in FIG. 1J) such that insulator layer 120defines the edges of the first conductor layouts 114 a and isolates afirst conductor layout from one another. As described above, the carrier110 is made from a material with high Young's modulus and isstress-relieved; by leaving a ring 110 b of the carrier on the substrate105, the carrier ring 110 b helps to maintain planarity of the finishedsubstrate 105, at the same time, providing rigidity to the finishedsubstrate 105 for handling and subsequent manufacturing. In anotherembodiment, the internal opening 110 a is smaller than a gang of moldedfirst insulator layers 120 so that a plurality of openings 110 a areformed on the carrier 110, instead of just leaving a carrier ring aroundthe entire substrate. In addition, in the peripheral area outside themolded area 120, the carrier ring 110 b is formed with positioning orfiducial holes 160 (as seen in FIG. 8); in addition, if the carrier 110is not stress-relieved before use, stress-relief slots 170 (shown inFIG. 8) may be stamped or formed in the peripheral area before theinternal portions 110 a are etched away. Advantageously, the peripheralarea of the carrier with positioning/fiducial holes or stress-relievedslots defines the clamping area for the above injection or compressionmolding of the first insulator layer 120, singulation of finishedsemiconductor packages or for other uses in other intermediatemanufacturing processes such that the required clamping areas arelocated away from the delicate molded areas that contain the first andsecond conductor traces and interconnecting studs, thus ensuring thatthe subsequent processes do not damage the molded area.

For simplicity of illustration, FIG. 2A shows the carrier ring 110 bbeing formed around a molded first insulator layer 120. As shown in FIG.2A, a semiconductor die 10 is connected to the first conductor layout114 a through solder bumps 20 and metal pillars 24 connections. Mountingof the die 10 is also strengthened by an underfill compound 30. In FIG.2B, after the die 10 is mounted on the substrate 105, the entire die isencapsulated in a molding 40. Preferably, the molding 40 is made from amaterial having similar or identical properties with the material of thefirst insulator layer 120 to minimize stresses created due to propertydifferences. Solder balls 22 may also be disposed in contact with theexposed second conductor layouts 128 b for external electricalconnection. In FIG. 2C, the encapsulated die is cut along singulationlines XX and YY to provide a finished semiconductor package 150containing the substrate 105 obtained by the process 100 of the presentinvention.

Instead of using solder bump connection, the die 10 may be wire-bondedto the first conductor layout 114 a, as shown in FIG. 3, and anotherfinished semiconductor package 150 a containing the substrate 105 isobtained by the above process 100. Further, as shown in FIG. 4, afinished semiconductor package 150 c may comprise two or more dies,passives or packages, including dies that are made using differentsemiconductor fabrication techniques.

Referring back to FIGS. 1J and 2C, around each first conductor layout114 a, some of the peripheral conductors 114 b are not electricallyconnected to the rest of the first conductor layout 114 a and areprovided to control electroplating. For example, the conductors 114 bmay act as “current stealers” to change the current distribution duringelectroplating of the studs 118 and/or second conductor trace layer 128a to achieve uniform electroplating thickness. Alternatively, theconductors 114 b are provided to change a stress distribution on thesubstrate 105 by changing the composite coefficient of thermal expansion(CTE) across the substrate area.

FIGS. 5 and 6 show variations in the structures of the aboveembodiments. For example, as shown in FIG. 5, before disposing theconductor seed layer 124, an adhesion layer 123 is applied on the groundsurface 122 of the molded first insulator layer 120 to promote adhesionof the second conductor trace layer 128 a. Preferably, the adhesionlayer 123 is a polyimide or woven glass fiber laminate. In FIG. 6, a topsurface of the substrate 105 is deposited with a soldermask 140 so thatselected areas of the first conductor trace layer 114 a are exposed forexternal electrical connection.

FIGS. 7A-7F show progressive buildup of a multi-layer substrate 105 acomprising three conductor trace layers. FIG. 7A shows continued buildupof the structure of the semi-finished substrate shown in FIG. 1G. Asshown in FIG. 7A, a second interconnect layer 218, comprising secondconductor studs 218, is formed on the patterned second conductor tracelayer 128 a by photolithographic and electroplating processes. In FIG.7B, the conductor seed layer 124 that are not built-up by the secondconductor trace layer 128 a is removed by chemical etching.

In FIG. 7C, the molded first insulator layer 120 on the semi-finishedsubstrate is over-molded with a second insulator molding 220. As in thefirst insulator layer, the second insulator molding also contains amatrix of resin and embedded inorganic silica fillers. The secondinsulator molding 220 can be the same size as the first insulatormolding 120. As shown in FIG. 7C, the second insulator molding 220 islarger and it encapsulates the first insulator molding 120 in aso-called molding-over-molding.

As in FIG. 1E, the free surface of the second insulator molding 220 isabrasively ground to provide a planar surface 222. The ground moldingsurface 222 also provides good adhesion for a second conductor seedlayer 224 to be deposited and a third conductor trace layer 228 a to bebuilt-up. When the third conductor trace layer 228 a is the outermostconductor trace layer of the finished substrate, the outermost conductortrace layer is sealed with a soldermask and selected areas of theoutermost conductor trace layer are then exposed, as seen in FIG. 7F,for external electrical connection.

In FIG. 7E, it is shown that an internal portion of the carrier 110 ispartially etched away to expose the first conductor trace layer 114 a sothat a reinforcement ring 110 b remains on the substrate 105 a beforethe processing on the substrate is completed. It is possible that thereinforcement ring 110 b is formed after processing on the substrate 105a is completed. The resulting substrate 105 a comprises a plurality ofinsulator layers adjoining to one another with each insulator layerhaving a corresponding (conductor elements) conductor trace layer and aninterconnect layer embedded within. A dividing plane parallel to thecontacting surfaces of the adjoining insulating layers lies in-betweentwo insulator layers such that the conductor trace elements in oneinsulator layer does not cross over the dividing plane to the adjacentinsulator layer. However, the conductor trace elements in eachcorresponding insulator layer are electrically connected to one anothersuch that the top surface of the substrate 105 a is electricallyconnected to the rear surface of the substrate. Specifically, theinterconnect layer in one insulator layer is electrically and physicallyconnected to the conductor trace layer of the adjoining insulatinglayer.

FIG. 8 shows a plan view of the substrate 105, 105 a as seen from thetop according to FIG. 1J or 7F. As seen in FIG. 8 through the opening110 a in the carrier 110, the first conductor trace layer 114 aillustrates a gang of 9 conductor layouts 114 a are encapsulated in amolding 120, 220. As described earlier, within each conductor layouts114 a, there are stand-alone conductors 114 b that are provided as“current stealers” to adjust the current distribution duringelectroplating; in addition these stand-alone conductors 114 b can beused to modify the composite coefficient of thermal expansion across thesubstrate to minimise any warpage due to thermal changes duringprocessing. In the clamping zone around the substrate 105, 105 a, thatis, through the thickness of the reinforcement ring 110 b, there arepositioning or fiducial holes 160 and stress-relief slots 170.

The above drawings illustrate forming multi-layer substrate with 2 and 3conductor trace layers. It is possible to obtain multi-layer substratewith more than 3 conductor trace layers by forming each additionalbuilt-up layer with a conductor trace layer and an interconnect studlayer and encapsulating these two component layers in a resin moldingcompound. With the present invention, the multi-layer substrates allowmore complex interconnect routing to support packaging of newsemiconductor chips. Advantageously, the multi-layer conductor tracescan also be separately designated to carry different types of signal orpower, for example, to reduce signal interference. As the feature sizesof the conductor layouts are not limited by the characters of etching,the multi-layer substrates according to the present invention alsoprovide an advance in achieving circuit miniaturization.

While specific embodiments have been described and illustrated, it isunderstood that many changes, modifications, variations and combinationsthereof could be made to the present invention without departing fromthe scope of the present invention. For example, it is possible to forma patterned via layer to connect a conductor trace layer with aconductor trace layer located two or more layers away in the built-upstructure of the substrate; this feature will provide an additionallevel of interconnect routing that is not possible with conventionalleadframes.

The invention claimed is:
 1. A semiconductor substrate comprising: afirst conductor trace layer; a second conductor trace layer; aninterconnect stud layer disposed between the first and second conductortrace layers, wherein studs connect selected areas between the first andsecond conductor trace layers; a resin compound encapsulating the firstconductor trace layer and the interconnect stud layer and beingabrasively ground to expose the studs; an adhesion layer disposed on theground surface of the resin compound, wherein the adhesion layercomprising polyimide or woven glass fiber; and a sacrificial carrierthat is electrically conductive and chemically etchable, wherein aninternal portion of the sacrificial carrier is etched away to expose thefirst conductor trace layer.
 2. A semiconductor substrate according toclaim 1, further comprising an insulating layer disposed on the secondconductor trace layer, wherein the insulating layer exposes areas of thesecond conductor trace layer for external electrical connections.
 3. Asemiconductor substrate comprising: a first conductor trace layer; asecond conductor trace layer; an interconnect layer disposed between thefirst and second conductor trace layers, wherein studs connect selectedareas between the first and second conductor trace layers; a resincompound encapsulating the first conductor trace layer and theinterconnect layer; an adhesion layer disposed between the resincompound and the second conductor trace layer to promote adhesion of thesecond conductor trace layer, wherein the adhesion layer comprisingpolyimide.
 4. A semiconductor substrate according to claim 3, furthercomprising an insulating layer disposed on the second conductor tracelayer, wherein the insulating layer exposes areas of the secondconductor trace layer for external electrical connections.
 5. Asemiconductor substrate comprising: a first conductor trace layer; asecond conductor trace layer; an interconnect layer disposed between thefirst and second conductor trace layers, wherein studs connect selectedareas between the first and second conductor trace layers; a resincompound encapsulating the first conduct trace layer and theinterconnect layer; a woven glass fiber laminate disposed between theresin compound and the second conductor trace layer.
 6. A semiconductorsubstrate comprising: two or more intermediate built-up layers, whereineach intermediate built-up layer comprising a conductor trace componentlayer and an interconnect stud component layer encapsulated in a resincompound, the interconnect stud component layer of one built-up layer isconnected to the conductor trace component layer of the adjacentbuilt-up layer; and an adhesion layer disposed between each pair ifbuilt-up layers, wherein the adhesion layer comprising, polyimide orwoven glass fiber.